The present invention relates to rubber based curable compositions.
Spot welding has been used in the past for structural support in doors, decklids and hoods of automobiles; however, these weld points are also sources of corrosion as well as cosmetic blemishes when done on exterior panels. Moreover, two-sided galvanized metals which are more frequently utilized do not readily lend themselves to spot welding. Automobile manufacturers have, therefore, moved away from spot welding by using it in conjunction with structural adhesives and in limited applications using the adhesives exclusively.
High strength structural adhesives are almost exclusively epoxy based compositions and although they have good structural integrity, they also have certain disadvantages, including spotty adhesion, variable corrosion resistance, lengthy cure times, poor oily metal grab, high cost and toxicity problems.
Induction heating of epoxy compositions was introduced and products were prepared to decrease cure times under these conditions. Induction curable products are generally lesser in ultimate performance properties to the slower curing epoxy counterparts, but are preferred when rapid curing is a priority. In spite of the flaws, e.g., lower strength, spotty adhesion and stability problems, these materials are becoming more and more important.
Rubber vulcanizable compositions are well known in the art and have been typified by excellent strength and elongation. While these formulations offer good cure properties and weathering resistance, their utility has been limited by indifferent adhesion to a variety of oily metals. When adhesion problems have been overcome, usually it has been by the addition of separate adhesion promoters such as organosilanes, phenolics, rosin acid or separate surface pretreatments, and still indiscriminate adhesion to a variety of metals and non-metallic substrates, oiled or unoiled, has in many cases not been accomplished.
Achieving adhesion of such rubber vulcanizable compositions to metals has been difficult and rarely is adhesion claimed to such diverse substrates as aluminum, cold rolled steel, sheet molding compound, zinc-coated metals and alloys thereof. Rubber vulcanizable compositions with high sulfur loadings capable of further enhancing the strength and hardness of the rubber also suffer from the same above problems and adhesion is either absent or very selective.
Functionalized rubbers, polymeric rubbers which have pendant groups such as hydroxyl, thiol, amine, carboxyl or epoxy, among others, have not been used to enhance adhesion but rather have been used 1) to impart to automobile tires a type of functional hysteresis effect wherein road grab is improved yet rolling resistance is not sacrificed, or 2) to participate in a separate distinct curing or crosslinking reaction.
In the instant invention, functionalized rubbers are used to prepare one component non-epoxy adhesives with high strength and adhesion to a wide spectrum of substrates and not for the inherent chemical reactivity of the functional group.